Actuator assembly

ABSTRACT

An actuator assembly includes a first housing portion and a second housing portion coupled to the first housing portion, which together define a housing having an interior. A beam, preferably of one-piece construction, extends from the interior of the housing to the exterior of the housing. A coil, pole piece, and magnet are positioned in the interior of the housing. Energizing the coil causes movement of the beam relative to the housing. The housing portions may be identical. The housing portions may be symmetrical about their edges of coupling.

FIELD OF THE INVENTION

The present invention relates to actuators, and more particularly, thisinvention relates to a fine positioning actuator assembly having a“clamshell” type housing surrounding a voice coil motor.

BACKGROUND OF THE INVENTION

Tape drives typically utilize an actuator mechanism to position theread/write head over the appropriate tracks while the tape is moving.Current read/write head positioning devices used in magnetic tape drivesoften incorporate a dual stage actuator design. One actuator providescoarse positioning to move the read/write head between data bands. Theother actuator provides fine positioning to maintain alignment betweenthe read/write head and the data tracks. In use, the coarse positioningactuator first moves the read/write head to the general vicinity on thetape and then the fine positioning actuator is used for track followingwhile the tape is in motion. The two actuators are usually mounted in a“piggyback” arrangement with the fine position actuator riding on thecoarse position actuator.

The coarse positioning actuator is typically a linear stage driven by astepper motor. Stepper motors have the ability to move the linear stageanywhere across the width of the magnetic tape at modest speeds.However, most stepper motors lack the accuracy and bandwidth necessaryto maintain alignment between the read/write head and the data tracks asthe magnetic tape moves across the face of the read/write head.

The fine positioning actuator is typically a voice coil motor (VCM)mounted on the linear stage and held at a rest position by some type ofspring. A VCM actuator provides micron to submicron precisionpositioning at a bandwidth of hundreds to thousands of hertz. However, asingle voice coil and spring combination that can meet the finepositioning requirements across the full width of the tape is expensiveand unnecessary. Accordingly, virtually all current tape drives use somecombination of a coarse positioning actuator and a fine positioningactuator.

In typical VCM actuator designs for tape drives, the housing must fullyencapsulate the magnet and pole piece of the VCM to protect the headfrom exposure to the stray field caused by the magnet. A beamsubassembly, which forms the connection between the coil and the headmust pass through a housing that acts as part of the VCM magnetic fluxpath. This has a result of limiting access to the coil within thehousing, requiring the physical connection between the coil and theread/write head to be made up of multiple parts, as well as assembled inmultiple steps. This in turn increases both manufacturing and assemblycost.

FIG. 1 illustrates a typical fine positioning VCM assembly 100 for atape drive system. The VCM assembly 100 includes a bottom cover 102 anda housing 104, which together act to contain the magnetic flux of theVCM so that the flux does not interfere with nearby electroniccomponents, especially the transducers on the head. A beam 106 supportsthe head in a support cradle 108, thereby allowing the VCM to positionthe head. The beam 106 is formed of multiple parts, including a topportion 110 and a support plate 112. The top portion 110 of the beammust be inserted through apertures in the housing 104 and coupled to thesupport plate 112. A coil 114 is then attached to the support plate 112of the beam 106. A pole piece 116 and magnet 118 are installed tocomplete the VCM. The bottom cover 102 is attached to the housing 104.

As should now be apparent, a typical VCM assembly 100 contains manyparts, and requires a substantial amount of precision assembly. What isneeded is a way to simplify assembly of a VCM, thereby reducing bothcost and complexity. What is also needed is a way to reduce the numberof unique parts needed to create a fine positioning actuator. Theseunresolved problems and deficiencies are clearly felt in the art and aresolved by this invention in the manner described below.

SUMMARY OF THE INVENTION

The present invention is a new actuator assembly that requires fewerunique parts and is easier to assemble than prior known VCM actuators.The new assembly features a “clamshell” type housing that, in manyembodiments, allows use of a one-piece beam while still allowing for thehousing to provide the necessary flux path as well as protection to theread/write head, thus reducing the overall actuator cost. Thus, theactuator assembly provides a compact, reduced cost design that exhibitsexcellent reliability.

An actuator assembly according to one embodiment includes a firsthousing portion and a second housing portion coupled to the firsthousing portion, which together define a housing having an interior. Abeam extends from the interior of the housing to the exterior of thehousing. A coil, pole piece, and magnet are positioned in the interiorof the housing. Energizing the coil causes movement of the beam relativeto the housing.

In a variation on the above, the housing portions are identical. In afurther variation, the housing portions are symmetrical about theiredges of coupling.

The beam is preferably a single, completed piece prior to assembly ofthe actuator assembly, thereby simplifying construction of the assembly.The beam can be formed of a single piece of plastic or a single piece ofmetal, and additional elements such as the coil can be formed integralwith the beam. However, the beam need not be a single piece, and someassembly of the beam can be performed for coupling the beam to thehousing portion(s) in some embodiments.

The actuator assemblies described herein are useful for tape drivesystems, and may further include a coarse positioning actuator coupledto the housing.

A tape drive system includes a head, a drive mechanism for passing amagnetic recording tape over the head, an actuator assembly as recitedabove coupled to the head, and a controller in communication with theactuator assembly.

Methods for making and using such assemblies and systems are alsopresented.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

Prior Art FIG. 1 is an exploded view of a fine positioning VCM assembly.

FIG. 2 is an exploded view of a fine positioning VCM assembly accordingto one embodiment.

FIG. 3 is a perspective view of the fine positioning VCM assembly ofFIG. 2 after assembly.

FIG. 4 is an exploded view of a fine positioning VCM assembly accordingto another embodiment.

FIG. 5 is a perspective view of the fine positioning VCM assembly ofFIG. 4 after assembly.

FIG. 6 is a perspective view of a coarse positioning actuatorimplemented in a tape drive system as seen from the tape medium side.

FIG. 7 illustrates a method for positioning a tape head relative to atape.

FIG. 8 is a schematic diagram of the tape drive system.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is the best mode presently contemplated forcarrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.Further, particular features described herein can be used in combinationwith other described features in each of the various possiblecombinations and permutations.

In the drawings, like and equivalent elements are numbered the samethroughout the various figures.

The description below discloses various embodiments of a new actuatorassembly that requires fewer unique parts and is easier to assemble thanprior known VCM actuators. The new assembly features a “clamshell” typehousing that allows use of a one-piece beam while still allowing for thehousing to provide the necessary flux path as well as protection to theread/write head, thus reducing the overall actuator cost. Thus, theinventive actuator assembly provides a compact, reduced cost design thatexhibits excellent reliability. To aid the reader and to place theactuator in a context, the following description shall be described interms of an actuator for positioning a tape head with respect to a tapepassing over the tape head. However, while the actuator has particularapplicability to tape drives, the actuator can be implemented in anysystem where actuation is needed.

FIGS. 2 and 3 illustrate a VCM actuator assembly 200 according to oneembodiment of the present invention. As shown, a beam 202, coil 204,pole piece 206, and magnet 208 are sandwiched between two housingportions 210 and 212 that together form the housing having an interiorand an exterior. When assembled, the magnet 208, pole piece 206, coil204, and part of the beam 202 are contained in the interior of thehousing, with the housing providing a portion of the magnetic path.

The beam 202 extends through slots 220 in the upper portion of thehousing and floats over the pole piece 206 and magnet 208 assembly. Whenthe coil 204 is energized, the beam 202 moves back and forth based onthe current in the coil 204 and the resulting magnetic interaction ofthe energized coil 204 with the magnet 208.

The separable nature of the housing portions 210, 212 allows the beam202 to be constructed as a one-piece, completed structure prior toassembly of the actuator. In other words, the completed beam 202 can beformed of a single piece of material, or can be assembled prior tocoupling with the housing, as opposed to previous methods where the beammust be partially assembled concurrently with the actuator as describedabove with reference to FIG. 1. Thus the inventive actuator assembly 200is less expensive and easier to assemble than prior actuators due to thefact that the housing portions 210, 212 are simply closed about thecompleted beam 202.

The beam 202 can be constructed of plastic, metal, or any other suitablematerial. Plastic is preferred, as the entire beam 202 can be molded inone step. A further benefit of plastic is that the coil 204 can beintegral to the beam, e.g., the coil can be insert-molded into a beamprimarily formed of plastic if desired, though typically the coil 204will be coupled to the beam 202, e.g., by adhesive, in a separateprocessing step. Further, by forming the beam 202 in one piece, aprecision part can be manufactured.

The magnet 208 is preferably cylindrical in periphery. Any suitablemagnetic material can be implemented in the magnet 208. The housinghelps to keep the flux contained to the actuator assembly 200, so thatit does not interfere with operation of the host device or data storedon the tape. The housing also helps prevent external magnetic fields,e.g., from the drive motors, from affecting the VCM.

The pole piece 206 is preferably a solid member having, but not limitedto, a cylinder-shaped outer surface, and that is designed to allow thecoil 204 to move the beam 202 within the desired range of motion. Thepole piece 206 is preferably constructed of a material capable ofchanneling the flux emitted by the magnet 208. Illustrative metals fromwhich the pole piece 206 can be constructed include iron and ironalloys, preferably low carbon steels. One preferred material is magneticstainless steel.

The coil 204 is adjacent the pole piece 206. The magnetic fieldgenerated by the pole piece 206, housing, and magnet 208 passes throughthe coil 204 in an orientation that will cause a displacement whencurrent is applied through the coil 204. The displacement causesmovement of the beam 202. An electrical connection couples the coil 204to a controller, the controller controlling the current through the coil204. The electrical connection may include coil control wiring 250 suchas a flexible cable, wires embedded in or otherwise coupled to the beam202, combinations thereof, etc. Note that the coil 204 is shown coupledto the beam 202. However, other VCM configurations than those shown herecan be used. For example, the coil 204 may be operatively coupled to thehousing, and the magnet 208 and pole piece 206 may be coupled to thebeam 202.

In a tape drive embodiment, the beam 202 includes a head mountingportion 224 that receives a magnetic head such as a tape head. As shownin FIG. 2, the head mounting portion 224 is parallel to but offsetlaterally from the axis of movement 226 of the beam 202 relative to themagnet 208 and pole piece 206. This allows the overall assembly 200 tohave a low profile. One skilled in the art will appreciate that the headmounting portion can be coupled at other locations on the beam 202, suchas above the beam 202 and generally aligned with the coil 204 and magnet208 generally parallel to the axis of movement 226.

Movement of the beam 202 is constrained by a constraining member 222,which preferably also holds the beam 202 in an at-rest position when thecoil 204 is not energized. An illustrative constraining member 222 is aleaf spring (as shown in FIGS. 2 and 3) coupled to a constraining membermounting portion 232 of one of the housing portions and a portion of thebeam 202 located outside the housing. To reduce torque effects, twoconstraining members 222 may be present, one coupled to each housingportion 210, 212. One skilled in the art will appreciate that many kindsof constraining members may be used, including rollers, rigid membershaving a resiliently deformable component (e.g., foam, coil springs,etc.) coupled between the beam 202 and the rigid member, piston andcylinder devices, etc. Additional options include a bushing and shaftarrangement with optional damping. Further illustrative constrainingmembers include friction-inducing members coupled to the housing or beam202.

The housing portions 210, 212 can take several forms. As discussedimmediately hereafter, the housing portions 210, 212 can be identical,symmetrical, or different.

In one embodiment, the housing portions 210, 212 are two identical partsto form the housing shell (as shown in FIG. 2). In other words, the twohalves of the housing can be designed to be identical parts for costreduction purposes, therefore essentially allowing one part to be usedfor both the left and right half of the housing assembly.

In another embodiment, the housing portions 210, 212 are about orexactly symmetrical relative to each other about their edges of coupling252, 254. Thus, the housing portions 210, 212 may not be the same part,but have about the same general shape. This embodiment may be usefulwhere the coarse positioner (described below) is coupled to one side ofthe assembly 200, e.g., opposite the head mounting portion 224.

In a further embodiment, shown in FIGS. 4 and 5, the housing portions210, 212 are not symmetrical or identical. Rather, one of the housingportions 212 surrounds more of the internal components of the assembly200 than the other portion 210.

The housing portions 210, 212 may include interlocking elements thatallow precise alignment of the housing portions 210, 212 relative toeach other. As shown in FIG. 2, the interlocking elements can include aflange 230 that is insertable in a corresponding groove or aperture (notshown) in the opposing housing portion. The interlocking elements mayalso provide frictional coupling of the housing portions 210, 212, suchas snap-locks, etc.

With continued reference to FIG. 2, the housing portions 210, 212 may beconstructed of any suitable material, keeping in mind that the housingmay form part of the flux path. The housing can be formed of the samematerial as the pole piece 206. Illustrative materials from which thehousing portions 210, 212 may be formed are low carbon steels. Onepreferred housing material is magnetic stainless steel.

The VCM assembly procedure is rather simple. During assembly, the coil204 is coupled to the completed beam 202 and connected to the coilcontrol wiring 250. Again, the coil control wiring 250 may be coupled tothe beam 202 or may be formed integral with the beam 202, etc. Themagnet 208, pole piece 206, coil 204, and beam 202 are inserted into oneof the housing portions 210, 212. The pole piece and magnet assembly maybe coupled to one of the housing pieces via an adhesive, threadedfasteners, frictional coupling, tongue and groove assembly, etc. ifdesired. Then, the other housing portion is added and coupled to thefirst housing portion to complete the assembly, via an adhesive,threaded fasteners, clamps, frictional coupling, etc. For further costreduction, the coil 204 and flexures (not shown) can be insert-molded aspart of the beam 202, thus further simplifying the assembly process andreducing the overall number of parts needed for the VCM.

A coarse positioning actuator of a type known in the art can be coupledto the completed assembly 200. Such coarse positioning actuatorstypically provide a greater range of motion than that of the beam of theVCM actuator assembly 200. The two actuators can be mounted in a“piggyback” arrangement with the fine position VCM actuator assembly 200riding on the coarse position actuator. One type of coarse positioningactuator is a linear stage driven by a stepper motor. Stepper motorshave the ability to move the linear stage anywhere across the width of amagnetic tape at modest speeds.

FIG. 6 is a perspective view of a coarse positioning actuatorimplemented in a tape drive system as seen from the tape medium (notshown) side. Referring to FIG. 6, the transducer (tape head) 601 ismounted on the carriage 602, which includes the VCM actuator assembly200. A resilient member (not shown) connects the carriage 602 to amoving frame 604. The resilient member can include flexures (not shown)made of thin metal strips that allow the carriage 602 to be displacedlaterally (as defined by the tape medium) but not longitudinally withrespect to the moving frame 604. Mechanical stops 608 and 610 are thetop and bottom surfaces respectively of the carriage 602. Stop abutments612 and 614 are inside surfaces of the moving carriage 604 opposite themechanical stops 608 and 610 respectively.

The moving frame 604 slides relative to the fixed frame 616 on two rails630 and 632 are guided by several guide bearings 634, 636, 638, 640.These guide bearings are rotatably mounted to the fixed frame 616. Oneof the bearings 636 is attached to the fixed frame 616 by a load arm 642and acts as both a guide bearing and the click. Two detent notches 618and 620 in rail 632 define two discrete positions for coarse positioningof the transducer 601.

Additional mechanical stops 644 and 646 and stop abutments 648 and 650are defined on surfaces of the moving frame 604 and fixed frame 616respectively. The mechanical stops 644-646 and the stop abutments648-650 mechanically limit the range of motion of moving frame 604 withrespect to the fixed frame 616. This keeps the rails 630 and 632 incontact with the guide bearings 634-640 and the guide/click bearing 636.

A motor 652 rotates a threaded shaft 654 of the actuator 656 that inturn causes movement of the carriage 602.

In use in a tape drive, the coarse positioning actuator first moves theread/write head to the general vicinity on the tape and then the finepositioning actuator 200 is used for track following while the tape isin motion. Once the target region on the tape has been reached by coarsepositioning, the coil will be activated to precisely position theread/write head over the desired location on the tape. During trackfollowing, the current in the coil is constantly adjusted to account forthe excursion of the tracks on the tape as well as the lateral motion ofthe tape while the tape is moving.

FIG. 7 depicts one method 700 for positioning a magnetic tape headrelative to a tape. In operation 702, a current is sent through a coarsepositioning actuator coupled to the magnetic head for finding servotracks on the tape. In operation 704, the coarse positioner is used toposition the magnetic head at about a desired position relative to amagnetic tape passing across the head. In operation 706, servo signalsare read from the magnetic head and used to determine how much currentto send through the coils. In operation 708, a current is sent throughthe fine positioner for keeping the magnetic head aligned with the servotracks as the magnetic tape passes thereby.

FIG. 8 illustrates a tape drive which may be employed in the context ofthe present invention. While one specific implementation of a tape driveis shown in FIG. 5, it should be noted that the embodiments of theprevious figures may be implemented in the context of any type of drive(i.e. hard drive, tape drive, etc.).

As shown, a tape supply cartridge 820 and a take-up reel 821 areprovided to support a tape 822. These may form part of a removablecassette and are not necessarily part of the system. Guides 825 guidethe tape 822 across a preferably bidirectional tape head 826. Such tapehead 826 is in turn coupled to a controller assembly 828 via an MRconnector cable 830. The controller 828, in turn, controls headfunctions such as servo following, write bursts, read functions, etc. Anactuator assembly 832, which includes a VCM assembly 200 as describedabove, controls position of the head 826 relative to the tape 822.

A tape drive, such as that illustrated in FIG. 8, includes drivemotor(s) to drive the tape supply cartridge 820 and the take-up reel 821to move the tape 822 linearly over the head 826. The tape drive alsoincludes a read/write channel to transmit data to the head 826 to berecorded on the tape 822 and to receive data read by the head 826 fromthe tape 822. An interface is also provided for communication betweenthe tape drive and a host (integral or external) to send and receive thedata and for controlling the operation of the tape drive andcommunicating the status of the tape drive to the host, all as will beunderstood by those of skill in the art.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. An actuator assembly, comprising: a first housing portion; a secondhousing portion coupled to the first housing portion, thereby togetherdefining a housing having an interior; a single-piece beam positionedbetween the housing portions and being movable relative thereto, thebeam extending from the interior of the housing to an exterior thereof;a coil positioned in the interior of the housing; a pole piecepositioned in the interior of the housing; a magnet positioned in theinterior of the housing, wherein energizing the coil causes movement ofthe beam relative to the housing portions.
 2. The actuator assembly asrecited in claim 1, wherein the housing portions are identical.
 3. Theactuator assembly as recited in claim 1, wherein the housing portionsare symmetrical about an edge of coupling thereof.
 4. The actuatorassembly as recited in clam 1, further comprising a head mountingportion coupled to the beam, the head mounting portion being adapted forreceiving a magnetic head.
 5. The actuator assembly as recited in claim1, wherein the beam is primarily constructed of at least one piece ofplastic or at least one piece of metal.
 6. The actuator assembly asrecited in claim 1, wherein the coil is formed as an integral portion ofthe beam.
 7. The actuator assembly as recited in claim 1, furthercomprising a constraining member for constraining movement of the beamrelative to the housing.
 8. The actuator assembly as recited in claim 1,further comprising a coarse positioning actuator coupled to the housing,the coarse actuator having a greater range of movement than the beam. 9.A tape drive system, comprising: a head; an drive mechanism for passinga magnetic recording tape over the head; an actuator assembly as recitedin claim 1 coupled to the head; and a controller in communication withthe actuator.
 10. An actuator assembly, comprising: a first housingportion; a second housing portion identical to the first housingportion, the second housing portion being coupled to the first housingportion thereby together defining a housing having an interior; a beampositioned between the identical housing portions and being movablerelative thereto, the beam extending from the interior of the housing toan exterior thereof; a coil positioned in the interior of the housing; apole piece positioned in the interior of the housing; a magnetpositioned in the interior of the housing, wherein, energizing the coilcauses movement of the beam relative to the housing portions.
 11. Theactuator assembly as recited in claim 10, further comprising a headmounting portion coupled to the beam, the head mounting portion beingadapted for receiving a magnetic head.
 12. The actuator assembly asrecited in claim 10, wherein the beam is a single structure whenpositioned between the first and second housing portions duringconstruction of the actuator assembly.
 13. The actuator assembly asrecited in claim 12, wherein the coil is coupled to the beam, whereinthe beam and coil are a single structure when positioned between thefirst and second housing portions during construction of the actuatorassembly.
 14. The actuator assembly as recited in claim 10, wherein thebeam is primarily constructed of at least one of a single piece ofplastic or a single piece of metal.
 15. The actuator assembly as recitedin claim 10, further comprising a constraining member for constrainingmovement of the beam relative to the housing.
 16. The actuator assemblyas recited in claim 10, further comprising a coarse positioning actuatorcoupled to the housing, the coarse actuator having a greater range ofmovement than the beam.
 17. A tape drive system, comprising: a head: adrive mechanism for passing a magnetic recording tape over the head; anactuator assembly as recited in claim 10 coupled to the head; and acontroller in communication with the actuator.
 18. An actuator assembly,comprising: a first housing portion; a second housing portion coupled tothe first housing portion thereby together defining a housing having aninterior, wherein the housing portions are symmetrical about an edge ofcoupling thereof; a beam positioned between the housing portions andbeing movable relative thereto, the beam extending from the interior ofthe housing to an exterior thereof; a coil positioned in the interior ofthe housing; a pole piece positioned in the interior of the housing; amagnet positioned in the interior of the housing, wherein energizing thecoil causes movement of the beam relative to the housing portions.
 19. Atape drive system, comprising: a head; a drive mechanism for passing amagnetic recording tape over the head; an actuator assembly as recitedin claim 18 coupled to the head; and a controller in communication withthe actuator.